A Section Mill And Method Of Removing A Section Of A Well Tubing

ABSTRACT

A section mill (10) and method of removing a section of tubular (150) from a well. The section mill includes elongate blades (14) which have a cutting structure (66) extending along at least a portion of a length from a first edge (62) and at least a portion of a width from a second edge (64) of the elongate cutter blade, the second edge being longer than the first edge, the first and second edges being perpendicular to each other. The blades are moved axially and radially relative to the tubular body (12) to arrange the second edge parallel to the central longitudinal axis (13) for milling Operation of the mill is in an upwards direction using a hydraulic tensioning device to provide a constant load so that milling of tubular can be achieved in a rigless arrangement.

The present invention relates to methods and apparatus for well abandonment and in particular, though not exclusively, to an apparatus and method for removing a section of tubular across a longitudinal section of the well to enable the placement of a cement plug.

When a well has reached the end of its commercial life, the well is abandoned according to strict regulations in order to prevent fluids escaping from the well on a permanent basis. In meeting the regulations it has become good practise to create the cement plug over a predetermined length of the well. As a well is constructed by locating conduits such as casing, lining, pipe and tubing (herein collectively referred to as tubulars) into the well, the cement plug must extend over all annuli present in the well. In many cases all conduits are removed leaving the outer casing, including the annulus bounded by the formation.

The integrity of the casing and in particular, the cement in an annulus will determine if a cement plug can just be located in the tubular. Steel casing can leak at the connections or corrode from acids. Cement can deteriorate with time too, but leaks also happen when cement shrinks, develops cracks or channels, or is lost into the surrounding rock when applied. If integrity fails, gases and liquids can leak out of the casing or, just as importantly, move into, up, and out of the well through faulty cement between the casing and the rock wall. These issues affect the ability to plug a well for abandonment but also for ensuring zonal isolation in unconventional reservoirs. Cement bond logging (CBL) can be used to log the quality of the cement bond but if the CBL shows the bond to be poor intervention is required with access needed to the outermost tubular.

One method of creating or repairing the cement plug is to mill away the inner tubular to expose the annulus behind the tubular and then pump cement into the enlarged area to create the cement plug. This is achieved using a rotatable section mill run on a work string and typically operated downwardly to remove the tubular section. In milling downwardly, the weight of the work string, is used to apply downward force to the section mill to cause it to progress through the tubular being milled. This application of force to the mill by weight applied from above creates a wobble in the milling work string, which has a tendency to fracture the cutting inserts on the section mill blades. This, in turn, causes the mill to wear out sooner, resulting in the removal of less tubular footage before replacement of the mill is required. Further, since milling progresses downwardly, cuttings must be removed from the well bore as they are formed, to avoid forming a ball of cuttings around the mill and reducing its effectiveness. Specialized formulation of milling fluid, and maintenance of proper fluid flow rates, are required in order to circulate the cuttings out of the hole.

To overcome these disadvantages an alternative method has been developed which perforates the tubular and pumps cement through the perforations to travel up the annulus and thereby create a plug within the annulus. This ‘perf and plug’ arrangement, sometimes referred to as cement squeeze, has disadvantages in that by forcing the cement through narrow apertures there is no guarantee that the cement fully contacts the surrounding formation as the cement may not reach all areas in the annulus. As a result, the cement plug may be compromised and rendered at least partially ineffective. This method does provide a major advantage in that it can be performed from a floating vessel or semi-submersible to offer what is referred to as a ‘rigless’ method of abandonment. By removing the requirement for a drilling rig, significant time and therefore costs can be made in the well abandonment procedure. In a rigless method the work string is anchored to the tubular and as such sea swell will place tension and/or weight on the work string. Even with the use of heave compensators, this variable load means that a section mill, reliant on using controlled weight to operate, cannot be used.

U.S. Pat. No. 6,679,328 discloses a method and apparatus for milling a section of casing in an upward direction, utilizing a downhole hydraulic thrusting mechanism for pulling a section mill upwardly. A downhole motor and torque anchor can be used to rotate the section mill, or the mill can be rotated by a work string. A stabilizer above the section mill can be used to stabilize the mill relative to the casing being milled. A spiral auger below the section mill can be used to move the cuttings downwardly. This method and apparatus provides the advantages of using a section mill in a rigless arrangement.

The section mill of U.S. Pat. No. 6,679,378 and typical section mills of the prior art use a plurality of arms arranged to lie within longitudinal slots in the body of the tool until milling is required. The arms are pivoted at one end so that a wedge, driven longitudinally through the body can force the arms to pivot outwards and contact the casing to be milled. In U.S. Pat. No. 6,679,378 a piston below the arms, within the tool body, is slidably disposed to move a wedge block upwardly against the lower ends and inner sides of the pivotable arms. A fluid flow passageway is provided through the tool body and through the piston, to a space within the tool body below the piston. Application of fluid pressure to this space exerts an upward hydraulic force, moving the piston and wedge block upwardly against the arms so that the arms pivot outwards and are supported by the wedge to prevent them from collapsing under heavy loading.

A disadvantage in using pivoted arms is that the depth of the cutting structure available is limited to the thickness of the arms which in turn is limited to the diameter of the tool body in which the arms must fit within for deployment. Consequently, only small sections of casing can be milled at a time before the section mill must be returned to surface for the cutters on the arms to be replaced.

In U.S. Pat. No. 6,679,328 the section mill arm can be fitted with a standard casing cutter type blade or the arm can be fitted with square type blades typically found on a pilot mill, to provide for milling an extended length of casing. However, in order for the square type blade to be used, the section mill of U.S. Pat. No. 6,679,328 must first be operated to penetrate the casing with the casing cutter type blade, then the arms are exchanged for arms having the pilot mill type blades, for the remainder of the procedure. This requires the section mill to be returned to surface for the cutters on the arms to be replaced. It is disadvantageous to make multiple trips into well. Additionally, the length of the pilot type mill blades is also limited as they are also pivotally mounted and must retract into the body of the tool.

It is therefore an object of the present invention to provide a section mill for removing a section of well tubing which obviates or mitigates at least some of the disadvantages of the prior art.

It is a further object of the present invention to provide a method of removing a section of well tubing which obviates or mitigates at least some of the disadvantages of the prior art.

According to a first aspect of the present invention there is provided a section mill for removing a section of well tubing comprising:

a tubular body;

a plurality of elongate cutter blades, each elongate cutter blade including a cutting structure extending along at least a portion of a length from a first edge and at least a portion of a width from a second edge of the elongate cutter blade, the second edge being longer than the first edge;

and an actuating mechanism to move the elongate cutter blades axially and radially relative to the tubular body between:

a first position wherein the elongate cutter blades are located inside the tubular body with the second edge being substantially parallel to the central longitudinal axis; and

a second position wherein the cutting structures are located outside the tubular body with the second edge being substantially parallel to the central longitudinal axis.

In this way, the cutter blades can be retracted for running in but then expanded to present close to the full length of the cutter blades for milling. By moving the cutter blades axially and radially rather than pivoting them from an end, the short edge (first edge) of the blade can mill the casing while the long edge (second edge) provides an extended depth to the mill to provide for milling an extended length of tubing. Thus only the first edge must be smaller than the diameter of the tool body, while the second edge can be any chosen length along the tubular body.

Preferably, the actuating mechanism comprises:

a first profile on a third edge opposite the second edge on each elongate cutter blade;

a second profile on an inner surface of the tubular body;

and a piston arranged to move the elongate cutter blade axially with respect to the tubular body so as to contact the first and second profiles and thereby move the elongate cutter blades from the first position to the second position.

In this way, a cam is used to extend the blades as opposed to the pivot used in the prior art. The cam allows the blades to be extended by a distance less than the diameter of the tubular body.

Preferably, the tubular body includes a plurality of longitudinally arranged elongate recesses spaced around a circumference of the tubular body wherein an elongate cutter blade is located in each recess. In a preferred embodiment there are three elongate cutter blades.

In this way, the elongate cutter blades can be supported during the rotational cutting action to maintain adequate torque.

Preferably, each elongate cutter blade includes a slot, in which a guide pin is located and can move therein. In this way, the movement of the each blade relative to the body is controlled and the final extended position of the blade is limited.

More preferably, each elongate cutter blade includes two slots in which guide pins are located respectively. In this way, the blade is held against the body, as the guide pins are fixed to the body, during actuation so that movement of the blades is determined by the first and second profiles.

More preferably, the piston is arranged on the central longitudinal axis in the tubular body. In this way, a single piston can act upon all the blades so that they move together.

Preferably, there is a chamber arranged at a first end of the piston. In this way, fluid pumped into the chamber can be used to move the piston. More preferably, there are one or more flow ports through the tubular body accessing the chamber. In this way, the piston can be arranged upstream of the cutter blades to support the cutter blades in the second position.

Preferably, the section mill includes a locking mechanism actuable to hold the elongate cutter blades in the second position. More preferably, the locking mechanism holds the piston in an extended position. In this way, fluid does not have to be continuously pumped to maintain the elongate cutter blades in the second position.

Advantageously, the second profile includes a ramp at a leading end thereof to move the elongate cutter blade to a mid-position between the first and second positions, wherein in the mid-position an apex where the first and second edges meet provides a cutting edge to cut through the tubing prior to milling. In this way, the section mill can provide both the initial cutting of the tubing and the milling of the tubing in a single trip in the well.

Preferably, the section mill further comprises a mill deployed indicator to let an operator know that the elongate cutter blades have reached the second position, the mill deployed indicator comprising a selectively sealed flow path through the piston wherein upon opening of the flow path a change in pressure will be detected at surface. Preferably, the mill deployed indicator comprises a flotel arranged to sit within and seal a bore of the piston, wherein the flotel is fixed to the body and movement of the piston will release the piston from the flotel at its furthest point of travel and thereby open the pathway and create the pressure change indication at surface.

According to a second aspect of the present invention there is provided a method of removing a section of well tubing, comprising the steps:

-   -   (a) providing a work string with a section mill according to the         first aspect, the section mill located in the first position,         and a hydraulic tensioning device, the hydraulic tensioning         device being adapted to pull a lower end of the hydraulic         tensioning device upwardly toward the work string, and the         section mill being attached below the lower end of the hydraulic         tensioning device;     -   (b) lowering the work string, the section mill and the hydraulic         tensioning device into a tubing to be milled;     -   (c) pumping fluid through the work string to actuate the section         mill and thereby move the elongate cutter blades to the second         position to locate the first edge at a lower end of the tubing;     -   (d) rotating the section mill to mill the tubing;     -   (e) pumping fluid through the work string to actuate the         hydraulic tensioning device so that a lower end of the hydraulic         tensioning device is hydraulically pulled upwardly toward the         work string, thereby pulling the section mill upwardly; and     -   (f) removing a section of the tubing by milling in an upward         direction.

In this way, a long section of tubing can be removed in an upward direction.

Advantageously, the work string is lowered from a floating vessel. In this way, a section of tubing can be removed in a rigless arrangement.

Preferably, the method includes the steps of:

-   -   (g) pumping fluid through the work string to actuate the section         mill and thereby move the elongate cutter blades to a         mid-position to locate a cutting edge, being an apex where the         first and second edges, against the tubing; and     -   (h) rotating the section mill to cut the tubing;

Preferably, steps (g) and (h) are undertaken prior to step (c). In this way, the tubing can be cut and milled in a single trip in the well.

Preferably, the method includes the step of locking the elongate cutter blades in the second position. In this way, milling can be undertaken regardless of the pressure of fluid through the work string.

Preferably, the method includes the step of providing a signal at surface that the elongate cutter blades have reached the second position. In this way, an operator will know that milling is occurring to be able to operate the hydraulic tensioning device.

Preferably the method includes the step of rotating the work string to rotate the section mill. More preferably the method includes the step of actuating a downhole motor to rotate the section mill.

In the description that follows, the drawings are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce the desired results.

Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term “comprising” is considered synonymous with the terms “including” or “containing” for applicable legal purposes.

All numerical values in this disclosure are understood as being modified by “about”. All singular forms of elements, or any other components described herein including (without limitations) components of the apparatus are understood to include plural forms thereof.

There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:

FIGS. 1A to 1G are views of a section mill in a first position according to an embodiment of the present invention;

FIGS. 2A to 2G are views of the section mill of FIGS. 1A to 1G, in a mid-position according to an embodiment of the present invention;

FIGS. 3A to 3G are views of the section mill of FIGS. 1A to 1G, in a second position according to an embodiment of the present invention; and

FIG. 4 illustrates a work string including the section mill of FIGS. 1A to 1G according to a further embodiment of the present invention.

Referring initially to FIGS. 1A to 1G of the drawings there is illustrated a section mill, generally indicated by reference number 10, having a tubular body 12, three elongate cutter blades 14 a-c, and an actuating mechanism 16, according to an embodiment of the present invention.

Tubular body 12 is of substantially cylindrical form around a central longitudinal axis 13 having at a first end 18, a threaded connection 20 for connecting the mill 10 to a work string (not shown). The second end 22 has a pin section connecting the body 12 to a bottom sub 24 which has a central bore 26 terminating at a nozzle 28 at a lower end 30 thereof. The bottom sub 24 may include connections to allow the mill 10 to be mounted in a work string with other tools or tubing below. The diameter of the tubular body 12 will be selected to fit within the tubing which requires to be milled.

Tubular body 12 includes three pockets or recesses 32 a-c. The number of recesses 32 will match the number of elongate cutter blades 14. While the figures show three elongate cutter blades 14, it will be realised that more or less could be used. Each recess 32 provides a longitudinally arranged slot 34 extending from an outer surface 36 of the body 12, through the body 12 over a majority of the diameter of the body 12. Each recess 32 passes to one side of the central axis 13. A base portion 38 of each recess 32 is shaped to provide a cam profile 40. Cam profile 40 includes first 42 and second 44 ramps angled to the longitudinal central axis 13. The first ramp 42 ends on a straight portion 43 with a dovetail 45 on an end of the recess 32. A side wall 46 of the recess 32 further includes a guide pin 48 fixed to the body 12.

Each elongate cutter blade 14 is substantially rectangular in shape providing a leading side face 50, a following side face 52, a top face 54, a bottom face 56, an outer face 58 and an inner face 60. This provides a first edge 62 between the top face 54 and the leading side face 50. A second edge 64 is between the outer face 58 and the leading side face 50. The first edge 62 is shorter than the second edge 64 as the first edge 62 cannot be greater than the diameter of the body 12 so that the blade 14 can be entirely located within the recess 32 and body 12. The second edge 64 provides a length for the blade 14 and as the blade 14 will not be pivoted it can be made as long as possible being mindful of loading over a cross sectional area equal to the top 54 and bottom 56 faces. In the embodiment shown the length of the second edge 64 is greater than twice the diameter of the body 12. The second edge 64 is also at least five times the length of the first edge 62. While the first edge 62 and second edge 64 are shown as perpendicular to each other it will be appreciated by those skilled in the art that the edges may be at an acute angle to each other.

The blade 14 includes a cutting structure 66 on the leading side face 50. The cutting structure 66 may be a portion of the blade 14 or be applied to a surface of the blade 14 as is known in the art. A cutting structure 66 may also be applied to other surfaces or parts thereof such as the top face 54 which is directed toward the first end 18 and the outer face 58. A length of the cutting structure 66 along the first edge 62 is greater than the thickness of the tubular intending to be milled. The length of the cutting structure 66 along the second edge 64 is over a majority of the length of the second edge 64 to provide a large length of cutting structure 66 with the length of the cutting structure 66 along the second edge being around ten times greater than the length along the first edge 62. At the apex 68 where the first 62 and second 64 edges meet, being the point where the leading side face 50, outer face 58 and top face 54 also meet, a pilot cutter 70 is provided. The pilot cutter 70 will be the first contact point with the tubing to be milled and provide a cut through the tubing before milling begins.

The inner face 60 of each blade 14 has a profiled surface which may also be considered as a cam profile 72. The recess cam profile 40 and the blade cam profile 72 abut and their interaction will dictate the movement of the blade 14 within the recess 32. Cam profile 72 has a leading curve 82, between the top face 54 and the inner face 60, a tip 84, a deflection ramp 86 and a trailing curve 88, between the inner face 60 and the bottom face 56.

On the following side face 52 of the blade 14, there is a first guide slot 74. The first guide slot 74 is aligned to be parallel to a portion of the cam profile 72. There is a second guide slot 76 through the blade 14 between the side faces 50,52 towards the bottom face 56. The first guide pin 48 locates within the first guide slot 74 and a second guide pin 78 locates within the second guide slot 76. The second guide pin 78 is fixed to a yoke 80, being a cam and blade retraction block, and this pin 78 therefore prevents the blade 14 detaching from the mill 10.

Below the recesses 32 is a centrally arranged tubular bore 92. The bore 92 has a diameter over a first portion which is sized to fit a piston 90 aligned within the bore 92. The bore 92 then has an expanded diameter to provide an annular chamber 94 between the bore 92 and piston 90 to contain a spring 96 for the piston 90 to act against. Bore 92 then has a greater diameter before narrowing to approximately the diameter of the central bore 26 for connection to the bottom sub 24. The portion with the greater diameter provides a fill chamber 98 below the piston 90.

Piston 90 has a first end 100 which is attached by a pin 102 to the yoke 80 and arranged to act upon the yoke 80. The piston 90 has a second expanded end 104 with a shoulder 106 facing the first end 100. The shoulder 106 acts on the spring 96 in the annular chamber 94. The piston 90 also has an inner bore 108 from the second end 104. The inner bore 108 includes a seat 110. There is a fluid pathway 112 between the inner bore 108 and recess 32. Additionally the outer surface 114 of the piston 90 includes a groove 116.

The piston 90 together with the cam profiles 40,72 provide the actuating mechanism 16 to move the blades 14 axially and radially out of and back into the recesses 32.

Locking pins 118, there are three in the embodiment shown but there may be any number, are arranged through the body 12 from the outer surface 36 to the bore 92, between the recess 32 and the annular chamber 94. The pins 118 abut the piston 90 until the groove 116 is aligned with them. At this position the pins 118 expand into the groove 116 and lock the piston 90 in position. When locked the blades 14 will be held in an extended or second position.

A flotel 120 is affixed to the bottom sub 24 and body 12 in the central bore 26. Flow bypass ports 122 are arranged through the flotel 120 to allow for fluid flow from the fill chamber 98 to the central bore 26 and to nozzle 28 to exit at the bottom sub 24. The flotel 120 has a flotel stem 124 arranged and sized to fit within the inner bore 108 of the piston 90. The flotel stem 124 has a nose 126 which seals in the seat 110 of the inner bore 108. The flotel 120 provides mill deployed indicator 142 as will described later in the operation of the mill 10.

There are longitudinally extending flow conduits 128 arranged from the first end 18 of the body 12 to the fill chamber 98. Flow conduits 128 are located away from the recesses 32 and thus multiple conduits 128 are required to provide sufficient fluid flow in the limited space provided through the body 12. In the embodiment shown there are six flow conduits but any number may be used. Additionally, the flow conduits 128 at the first end may be connected to any fluid source. It is preferably that they are arranged to access a bore of the work string so that the mill 10 can be operated by pumping fluid through the work string from surface.

In use, the mill 10 is assembled as shown in FIGS. 1A to 1G. FIG. 1A is a plan view showing the outer surface 36 of the body 12 and a recess 32 with a blade 14 arranged therein. FIGS. 1B and 1C are longitudinal cross-sections through the mill as sections A-A and B-B as illustrated on end views FIGS. 1F and 1G, respectively. FIG. 1D is a longitudinal cross-section through the mill on section D-D as illustrated on FIG. 1E, which is itself a cross-sectional view of section C-C as shown on FIG. 1A.

The blades 14 sit entirely within the recesses 32 with the second edge 64 lying parallel to the central axis 13. The first edge 62 is perpendicular to the central axis 13. The first guide pin 48 is located at a first end 130 of the first guide slot 74 and the second guide pin 78 is located at a second end 132 of the second guide slot 76. The leading curve 82 of cam profile 72 rests on the first ramp 42 of cam profile 40. The piston 90 is within the bore 92 with the spring 96 in a fully expanded configuration so that annular chamber 94 is at its maximum size. Groove 116 on piston 90 is located within the annular chamber 94 and therefore the locking pins 118 are retracted and allow the piston to move relative to the body 12. The nose 126 of the flotel stem 124 is sealed on the seat 110 holding the piston 90 in position against the spring 96 force.

FIGS. 1A to 1G show the mill 10 in a first position. This position, with the blades 14 retracted, is used for running the mill 10 into the tubing to be milled.

When the mill 10 is at the location for milling to begin, fluid is pumped down the flow conduits 128 and circulation commences through the mill 10. The mill 10 is also rotated. This may be by rotating the work string or by using a motor on the work string to rotate a portion of the work string containing the mill 10. Fluid circulates down the conduits 128 into the fill chamber 98, through the bypass ports 122 and nozzle 28 to exit the sub 24. Circulation pressure is controlled by the nozzle 28, with the maximum pressure available being determined by the size of the bypass ports 122 on the flotel 120 and nozzle 28. Fluid pressure will build up in the fill chamber 98 and act on the second end 104 of the piston 90. The piston 90 will begin to move through the bore 92 towards the first end 18. The flotel nose 126 will be off the seat 110 providing a circulation path through the inner bore 108 and fluid path 112 in the piston 90 to the recess 32. In this way the piston 90 is stroked upwards.

As the piston 90 is attached to the yokes 80, these will push against the bottom face 56 of each blade 14. Consequently the blade cam profile 40 is forced over the recess cam profile 72, causing the leading curve 82 to move up the first ramp 40 and the deflection ramp 86 to move up the second ramp 44. This movement forces each blade 14 upwards, axially towards the first end 18, and outwards radially from the central axis 13. The movement is controlled by the first guide slot 74 moving past the first guide pin 48. In this way, the apex 68 moves radially outwards first as the second guide pin 78 remains at a second end 132 of the second guide slot 76. Thus the pilot cutter 70 will contact the tubular and will cut the tubular circumferentially as the mill 10 is rotated.

This position of the blades 14 may be considered as a mid-position and is shown in FIGS. 2A to 2G. It is noted that the flotel stem 124 still lines within the inner bore 108 of the piston 90.

Continued circulation and rotation will bring the leading curve 82 onto the straight portion 43 of the cam profile 40. At this position, the deflection ramp 86 is supported on the upper point of the second ramp 44 and the bottom face 56 will begin to move radially outwards. The second guide pin 78 is now moved through the second guide slot 76 to control this radial movement. The apex 68 will be at its most extended position and will have cut through the tubular. Flow through the fluid pathway 112 to the recess will be used to wash cuttings clear.

The blade 14 will be moved upwards during this process so that the cutting structure 66 on the leading side face 50 and at first edge 62 will mill the tubular in an upward direction. Additionally the cutting structure 66 on the leading side face 50 and the second edge 64 will mill through the tubing as the second edge 64 is moved into a longitudinal orientation. If desired the work string can be raised to assist in moving the mill 10 upwards so the top face 54 is used to open a window in the tubular for the entire blade 14 to fit within.

Once on the straight portion 43 of cam profile 40, the top face 54 of each blade 14 will rotate to be perpendicular to the central axis 13 and locate within the dovetail 45. The dovetail 54 provides a blade lock. The tip 84 is now supported on the first ramp 42. The trailing curve 88 on the cam profile 40 is moved outwards until it meets a corresponding curve 134 on the yoke 80. As the curves 88,134 move across each other the blade 14 is lifted out of the recess 32 and the yoke 80 slides under the blade 14 to seat the bottom face 56 of the blade 14 in a pocket 136 of the yoke 80.

The blade 14 is thus fixed from longitudinal movement by virtue of the top face 54 being located in the dovetail 45 and the bottom face 56 being held in the pocket 136. At this position the first guide pin 48 is now at a second end 138 of the first guide slot 74 and the second guide pin 78 is at the first end 140 of the second guide slot 76. The yoke 80 has also met a stop 141 on the base 38 of the recess 32.

The second edge 64 is again lying parallel with the central axis 13. This can be considered as a second position and is illustrated in FIGS. 3A to 3G. the blades 14 are now at their maximum extension.

Continued circulation and rotation while raising the mill 10 relative to the tubular will mill a section of the tubular via the top first edge 62. Wear to the top face 54 during milling will cause erosion of the blade 14 along the cutting structure 66. However as the second edge 64 is significantly longer than prior art blades, the mill 10 can be used until the entire cutting structure 66 is removed along the length of the second edge 64.

To assist in milling, the blades 14 can be locked in the second position. This is achieved when the groove 116 on piston 90 is moved in line with locking pins 118. This is arranged to occur with the piston 90 holding the blades 14 in the second position. The pins 118 will expand into the groove 116 and prevent movement of the piston 90. Thus circulation can be stopped or adjusted without loss of milling action.

If the blades 14 need to be retracted, stopping circulation and rotation and then applying an overpull on the mill 10 will overcome the pins 118, moving them back into their retracted position as the piston 90 moves towards the second end 22 and the blades 14 are brought back into the recesses 32 in a reverse motion from that which extended them.

A further feature in moving the blades to the second position is in operating the mill deployed indicator 142. When the piston 90 has moved to the first end over a distance sufficient to actuate the blades to the fully extended position and lock the piston 90 in this position by virtue of the locking pins 118, the flotel nose 126 will be clear of the piston 90. At the point where the nose 126 clears the second end 104 of the piston 90, there will be a sudden drop in circulated fluid pressure. This pressure drop can be detected at surface and indicates to a user that the blades 14 are fully deployed and that raising the work string will mill the tubular.

Reference is now made to FIG. 4A of the drawings which illustrates the section mill 10 inside a tubular 150, such as liner or production tubing in which section of the tubular 150 is desired to be milled. In this example tubular 150 is located within an outer tubular 152, such as casing. It will be realised that there need not be an outer casing 152 and the tubular 150 can be the only tubular and may be cemented in place. Section mill 10 is shown in combination with a hydraulic tensioning device, being an up-thruster tool 166, an anti-torque tool 174, and a downhole motor 172, mounted to a work string 162. The apparatus 160 is tripped into the hole to position the section mill 10 at the lower end of the interval where a section of tubular 150 is to be cut. The section mill 10 is at the bottom of the apparatus 160, with a stabilizer 168, an up-thruster 166, a mud motor 172, and an anti-torque anchor 174 positioned above that, in order. A spiral auger 170 with a left hand twist can be positioned below the section mill 10, to assist in moving the cuttings downhole, as shown by the lower arrows.

The hydraulic tensioning device 166 is disclosed in U.S. Pat. No. 6,679,329 as an up-thruster. U.S. Pat. No. 6,679,329 is incorporated herein by reference. The purpose of the device 166 is to supply a constant upward load on the section mill 10. If a mud motor 172 were used to drive the mill 10 without the device 166, the loading imparted by the work string operated from a floating vessel to lift the mill 14 and cut into the tubular 150, would be too erratic. The operator would have to be extremely careful not to overload the mill 10, otherwise the mud motor 172 would stall out. The device 166 is a hydraulic cylinder pressurized by the mud flow which is pumped through a fluid flow path in the anti-torque anchor 174, the mud motor 172, the device 166, and on down through the section mill 10.

Drilling mud passes through the section mill 10 below the up-thruster 166, as described above to operate the mill 10. When the mill needs to be moved upwards a flow restriction creates a back pressure in the apparatus 160. This back pressure is used to cause the device 166 to lift upwardly on the section mill 10. With a tensioning device 166 in the apparatus 160, the pump pressure can be controlled in such a fashion that loading on the mill 10 is very constant, and loading can be imparted with much more precision.

In use, the anti-torque anchor 174 is set against the innermost tubular 150 as the milling fluid pressure is increased, which also starts the mud motor 172 running and exerts an upward force on the section mill 10 with the device 116. Fluid pressure operates the blades 14 in the mill 10 as described hereinbefore moving the blades 14 to a mid-position in which the pilot cutter cuts through the inner tubular 150 as shown in FIG. 4A and FIGS. 2A to 2G. The mill 10 is rotated by the downhole motor 172. The torque anchor 174, mud motor 172, tensioning device 166, stabilizer 168, and section mill 10 can have the sizes and shapes of their fluid flow paths designed to initiate their respective operations at selected progressive pressure levels, to insure the desired sequence of activation of the various tools. The section mill 10 can be set to extend the blades 14 at a relatively low pressure, so that the blades 14 will extend to the mid-position and cut the tubular 150 before the tensioning device 166 begins to lift mill 10 so as to mill the tubular 150. Additionally, the motor 172 can be designed to bypass fluid before it begins to rotate. As a result, the blades extend to the mid position, then the torque anchor blades 154 contact the tubular wall, then the mud motor 172 begins to rotate, and finally, the up-device 166 begins to lift the section mill 10. On the first cut, the tubular is cut through. Continued circulation and some lifting by the device 166 will cause milling of a window large enough to fit the now fully extended blades 14, see FIGS. 3A to 3G. When fully extended, the cutting structure 66 and the top face 54 will mill the lower end 156 as the device 166 moves the section mill 10 upwards. Milling will continue until the device 166 reaches its full travel, or “bottoms out”. A pressure drop will be noted in the milling fluid at this time.

Then, the milling fluid pressure is reduced, to stop rotation of the mud motor 172, release the anti-torque tool 174, and allow the device 116 to extend to its original length. The work string 162 is then lifted to raise the section mill 10 until the top face 54 of the blades 14 are located at the lower end 156 of the milled tubular 150. Pressure is then increased to reset the anti-torque anchor 174, rotate the mud motor 172, apply upward pressure to the mill 10, and resume milling. This process is then repeated as required. In this way, a section of tubular of desired length, for example, 250 feet, is cut out of the inner tubing 150. This is as shown in FIG. 4B. Use of this method insures that the drill pipe is held in tension at all times, thereby eliminating wobble in the work string 162. Pump pressure is regulated to keep a regulated upward force on the blades 14, by means of the tensioning device. Cuttings can also be dropped down hole, since milling is moving in the upward direction, eliminating the necessity to circulate the cuttings out of the hole. The procedure is continued until milling of the desired section length is complete. Thus cutting and milling of the section of tubing can be completed in a single trip into the well.

In an alternative embodiment, the work string is rotated to operate the mill and the anti-torque anchor 174 and mud motor 172 are not used.

It is noted in FIGS. 4A and 4B that as the blades 14 of the mill 10 extend as described hereinbefore with reference to FIGS. 1,2 and 3, the outer tubular 152 is not cut or milled during the operations. This is because the blades 14 of the present invention are not pivoted to swing outwards from a fixed point on the tool body as for the prior art. The blades in the present invention move axially and radially outwards relative to the tool body. The length of the blades that can erode during milling is now arranged longitudinally as opposed to being restricted to the thickness of the blades of the prior art which are limited to the diameter of the tool body.

The principal advantage of the present invention is that it provides a section mill in which the fullest length of the blades can be used to extend the section of tubular which can be milled on a single trip in a well.

A further advantage of an embodiment of the present invention is that it provides a section mill in which the blades are axially and radially displaceable relative to the tool body by use of a cam and not pivoted about a fixed point on the tool body.

A still further advantage of an embodiment of the present invention is that it provides a section mill which can first cut the tubing and then mill a section of the tubing on a single trip in a well in a rigless arrangement.

The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention herein intended. For example, while the section mill is described for upward movement to mill the tubular, the section mill could be adapted to operate in a downward fashion also. 

1. A section mill for removing a section of well tubing comprising: a tubular body; a plurality of elongate cutter blades, each elongate cutter blade including a cutting structure extending along at least a portion of a length from a first edge and at least a portion of a width from a second edge of the elongate cutter blade, the second edge being longer than the first edge, the second edge being longer than the first edge; and an actuating mechanism to move the elongate cutter blades axially and radially relative to the tubular body between: a first position wherein the elongate cutter blades are located inside the tubular body with the second edge being substantially parallel to the central longitudinal axis; and a second position wherein the cutting structure is located outside the tubular body with the second edge being substantially parallel to the central longitudinal axis.
 2. The section mill according to claim 1 wherein the actuating mechanism comprises: a first profile on a third edge opposite the second edge on each elongate cutter blade; a second profile on an inner surface of the tubular body; and a piston arranged to move the elongate cutter blade axially with respect to the tubular body so as to contact the first and second profiles and thereby move the elongate cutter blades from the first position to the second position.
 3. The section mill according to claim 1 or claim 2 wherein the tubular body includes a plurality of longitudinally arranged elongate recesses spaced around a circumference of the tubular body wherein an elongate cutter blade is located in each recess.
 4. The section mill according to claim 1 wherein there are three elongate cutter blades.
 5. The section mill according to claim 1 wherein each elongate cutter blade includes a slot, in which a guide pin is located and can move therein.
 6. The section mill according to claim 5 wherein each elongate cutter blade includes two slots in which guide pins are located respectively.
 7. The section mill according to claim 2 wherein the piston is arranged on the central longitudinal axis in the tubular body.
 8. The section mill according to claim 2 wherein there is a chamber arranged at a first end of the piston.
 9. The section mill according to claim 8 wherein there are one or more flow ports through the tubular body accessing the chamber.
 10. The section mill according to claim 1 wherein the section mill includes a locking mechanism actuable to hold the elongate cutter blades in the second position.
 11. The section mill according to claim 2 wherein the second profile includes a ramp at a leading end thereof to move the elongate cutter blade to a mid-position between the first and second positions, wherein in the mid-position an apex where the first and second edges meet provides a cutting edge to cut through the tubing prior to milling.
 12. The section mill according to claim 2 wherein the section mill further comprises a mill deployed indicator to let an operator know that the elongate cutter blades have reached the second position, the mill deployed indicator comprising a selectively sealed flow path through the piston wherein upon opening of the flow path a change in pressure will be detected at surface.
 13. (canceled)
 14. A method of removing a section of well tubing, comprising the steps: (a) providing a work string with a section mill according to claim 1, the section mill located in the first position, and a hydraulic tensioning device, the hydraulic tensioning device being adapted to pull a lower end of the hydraulic tensioning device upwardly toward the work string, and the section mill being attached below the lower end of the hydraulic tensioning device; (b) lowering the work string, the section mill and the hydraulic tensioning device into a tubing to be milled; (c) pumping fluid through the work string to actuate the section mill and thereby move the elongate cutter blades to the second position to locate the first edge at a lower end of the tubing; (d) rotating the section mill to mill the tubing; (e) pumping fluid through the work string to actuate the hydraulic tensioning device so that a lower end of the hydraulic tensioning device is hydraulically pulled upwardly toward the work string, thereby pulling the section mill upwardly; and (f) removing a section of the tubing by milling in an upward direction.
 15. The method of removing a section of well tubing according to claim 14 wherein the work string is lowered from a floating vessel.
 16. The method of removing a section of well tubing according to claim 14 wherein the method includes the steps of: (g) pumping fluid through the work string to actuate the section mill and thereby move the elongate cutter blades to a mid-position to locate a cutting edge, being an apex where the first and second edges, against the tubing; and (h) rotating the section mill to cut the tubing.
 17. The method of removing a section of well tubing according to claim 16 wherein steps (g) and (h) are undertaken prior to step (c).
 18. The method of removing a section of well tubing according to claim 14 wherein the method includes the step of locking the elongate cutter blades in the second position.
 19. The method of removing a section of well tubing according to claim 14 wherein the method includes the step of providing a signal at surface that the elongate cutter blades have reached the second position.
 20. The method of removing a section of well tubing according to claim 14 wherein the method includes the step of rotating the work string to rotate the section mill.
 21. The method of removing a section of well tubing according to claim 14 wherein the method includes the step of actuating a downhole motor to rotate the section mill. 